As the term suggests, the cells in open-cell spray foam insulation are deliberately left open and are not closed. In other words, the cells are not fully encapsulated.
Open-cell spray foam insulation is more flexible than closed-cell spray foam and it also expands much more. Open-cell spray foam is also springier than closed-cell spray foam. Has an R-value that is around R-3.5 per inch and can expand up to 3 inches in thickness after it is sprayed.
Open-cell spray foam insulation is used in areas where closed-cell spray foam is difficult to use or cannot be used.